Product produced by coating a substrate with an electrically conductive layer

ABSTRACT

A method for coating a substrate, preferably of glass, with a pyrolyzed transparent, electroconductive layer. The coating is comprised of indium formate, optionally mixed with a powdered or gaseous tin compound or a gaseous organotin compound. The coating layer is deposited upon a hot substrate whereupon it pyrolytically decomposes, forming a layer which is subsequently heat treated in a reducing or an oxidizing atmosphere to optionally enhance the low emissivity and low resistivity of the coating or reduce said low emissivity and low resistivity properties.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.06/821,365, filed Jan. 22, 1986, now U.S. Pat. No. 4,859,499.

TECHNICAL FIELD

This invention concerns the preparation of a metal based powder and amethod for pyrolytically depositing it upon a substrate to form atransparent coating with low emissivity and good electrical conduction.

BACKGROUND ART

To enable a pulverulent metal compound to form a high quality coating ona substrate, the powder must be uniformly distributed, it musteffectively decompose at a temperature below about 650°-700° C. if thesubstrate to be coated is glass and further, the compound must contain asufficient proportion of metal so as to quickly form an oxide layer ofappreciable thickness, particularly if the substrate is moving rapidlyin relation to the powder distribution means, as is the case for a glassribbon at the outlet of a float bath.

Coatings of tin oxide on glass substrates, produced by the pyrolysis ofdibutyltin oxide (DBTO) or dibutyltin fluoride (DBTF) powders arefrequently employed with a view to reinforcing the surface of the glass,staining it and for providing such surfaces with specific optical and/orelectrical characteristics, most notably, low emissivity. The use ofpowdered DBTO to produce such coatings is disclosed in French PatentApplication Nos. 2,380,997 and 2,391,966 whereas the use of DBTF isdisclosed in European Patent No. 39,256 and French Patent ApplicationNo. 2,542,636.

While both dibutyltin oxide and dibutyltin fluoride powders are capableof forming satisfactory layers, such layers develop colored reflectionswhen they are deposited in the thickness necessary to obtainadvantageous electronic properties. Further difficulties arise becauseslight variations in the thickness of the layers causes colorirregularities and further, the color which is produced is often eithernot aesthetically pleasing or it may not be adapted to the style of thesurrounding structure.

In order to obtain perfect color uniformity the reaction conditionsunder which the DBTO and DBTF powders are deposited must be scrupulouslymonitored. In particular, the powder must be of a consistent highquality and the spraying mechanism utilized to distribute the coatingmust be precisely adjusted so as to deposit a constant amount of powderupon the substrate.

In order to prevent the development of colored films on glass substratesand to avoid the necessity of implementing stringent monitoringtechniques which are both expensive and time-consuming, applicants havedeveloped a method wherein a powder containing indium formate may bedistributed upon a hot substrate such as a glass ribbon passing theoutput of a float bath and which, upon the resultant pyrolysis of thepowder, forms a thin, transparent, electroconductive coating upon thesubstrate.

Moreover, the pyrolysis of the indium formate compound ay be performedwith a sufficiently high degree of efficiency so as to be compatiblewith the rapid passing of the substrate past the point at which thecoating is produced. This is in contrast to prior attempts at depositingpyrolyzed indium compounds upon glass substrates wherein solubilizedindium acetylacetonates were found to pyrolyze at speeds insufficientfor depositing a metallic oxide coating on a glass ribbon passing theoutput of a float bath at high speed.

SUMMARY OF THE INVENTION

This invention concerns the preparation of a metal based powder and amethod for pyrolytically depositing this powder upon a substrate inorder to form a transparent coating with low emissivity and goodelectrical conduction.

A method for coating a substrate, such as glass, metal, ceramic or otherrefractory materials with a pyrolyzed metal oxide coating comprisesdepositing a predetermined amount of indium formate upon the surface ofa heated substrate so as to pyrolyze the indium formate, thus forming acoating of indium oxide on the surface of the substrate.

The indium formate may be deposited upon the surface of the substrate asa powder or it may first be disolved in a suitable solvent such asmethyl alcohol prior to the deposition step.

Applicants have also developed a novel method of producing the necessaryindium formate which comprises reacting an indium compound with aninorganic acid, such as hydrochloric or nitric acid to form an indiumsalt, reacting the indium salt with ammonia so as to form an indiumhydroxide precipitate, washing and drying the resultant precipitate andreacting the indium hydroxide precipitate with formic acid so as toproduce indium formate.

When the substrate is glass, such as a glass ribbon at the outlet of afloat bath, the substrate should only be heated to a temperature belowabout 650°-700° C. prior to the deposition of the coating.

In an alternate embodiment of the method the indium formate may be mixedwith at least one compound having a decomposition temperature on thesame order as that of indium formate prior to depositing the compositiononto the surface of the heated substrate. This compound may be apowdered tin compound such as dibutyltin oxide or dibutyltin fluoride, agaseous tin compound such as SnCl₄ or a gaseous organotin compound suchas BuSnCl₃. When powdered tin compounds are mixed with the indiumformate, they are added in proportions ranging between about one andthirty percent by weight.

A further embodiment of the invention concerns a method for forming atransparent electroconductive coating on a substrate. The methodcomprises preparing a metal composition containing indium formate or amixture of indium formate with one or more of the powdered or gaseoustin compounds or the gaseous organotin compound discussed above,depositing this composition onto the surface of a heated substrate, suchas glass, metal, ceramic or other refractory material, in order topyrolyze the composition and then heating the coated substrate toenhance the properties of the layer.

The coating may be deposited upon the substrate as a powder or it mayfirst be dissolved in a suitable solvent such as methyl alcohol beforebeing deposited. When the composition is to be deposited upon thesubstrate as a powder, it must first be suspended in a carrier gas andthe carrier gas with the suspended powder particles is then directedagainst a surface of the substrate so as to deposit the powder upon thesubstrate.

There are various methods by which the coated substrate may be heated soas to enhance properties such as the transparency, emissivity andelectrical conductivity of the coating. One method concerns maintainingthe coated substrate in a heated enclosure for a predetermined period oftime. The atmosphere in the enclosure may be a reducing atmosphere so asto promote the formation of a metal coating or to enhance the lowemissivity and low conductivity properties of the coating or it mayconsist of an oxidizing atmosphere to increase the emissivity andconductivity of the coating.

Alternatively, the coated substrate may be heat treated by subjectingthe coated surface of the substrate to an intense heat delivered by aburner tip of the type illustrated in the attached drawing figure, forless than one second. The heat treatment may occur on the line formanufacturing coated glass or out of this line at any time after themanufacture of said coated glass.

Alternately, preselected areas of the coating may be subjected todifferent degrees of heating so as to obtain a coating layer havingportions with differing emissivity, transparency and electricalconductivity.

BRIEF DESCRIPTION OF THE DRAWING

Further benefits and advantages of the invention will become apparentfrom a consideration of the following description given with referenceto the accompanying drawing figure which is a perspective view of aburner used to provide an intense heat of short duration according toone of the embodiments of the invention described herein.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a method for preparing an indium formatepowder as well as a method for depositing an electrically conductivecoating containing indium formate upon a substrate such as a glassribbon passing at high speed at the outlet of a float bath. Otherpossible substrates may include metals, ceramics or other refractorymaterials. By an electrically conductive coating, applicants mean ametal based coating comprising any compound whose thermal decompositiontemperature is of the same order as indium formate.

While indium formate may be the sole metallic component of the powderused in the method of the invention, it may also be associated with oneor more metallic constituents having a decomposition temperature on thesame order as that of indium formate.

The process proposed herein for producing indium formate comprisesreacting the indium with an acid such as hydrochloric acid (HCl),precipitating indium hydroxide by reacting the salt thus formed withammonia at a temperature close to boiling, washing and then drying theprecipitate and then reacting it with formic acid.

The reaction process may be summarized according to the followingequations, utilizing, for example, hydrochloric acid to react with theindium: ##STR1##

One skilled in the art will realize that various other acids, such asnitric acid (HNO₃) may be used in place of hydrochloric acid.

In order to obtain sufficiently conductive layers, it is advantageous tocombine tin compounds with the indium formate powder, in particulardilutyltin fluoride (DBTF) and dibutyltin oxide (DBTO), in proportionsthat may range up to about 30 weight percent. These compounds actuallyserve as cationic dopants of the indium oxide because replacement of anindium atom with a tin atom introduces a free electron into the layer.The density of the charge carriers and the electrical conductivity ofthe layer are also concurrently increased due to this doping effect.

The indium formate powder or powder mixture may be sprayed onto asubstrate, particularly a glass ribbon, with a nozzle. Examples of suchnozzles are described in French Patent Application Nos. 2,542,636 and2,542,637 preceded by the distribution device described in French PatentApplication No. 2,548,556.

The doping may also be performed with gaseous compounds, such as SnCl₄or gaseous organotins such as BuSnCl₃. When utilizing compounds of thistype the powder must initially be suspended in a gas while the dopingagent is subsequently mixed with the resultant suspension and/or withthe gasses which serve as accelerants and/or homogenates of the powder.The doping agent chosen may also be aspirated by a nozzle arrangementfound in a control chamber such as that disclosed in French PatentApplication No. 2,542,636, and/or delivered at the exit of the nozzle bya special duct.

Subsequent to this pyrolytic deposition of the metallic oxide layer uponthe substrate, the coated substrate advantageously undergoes a heattreatment in order to modify the properties of the coating. Dependingupon the parameters chosen for this operation this treatment may eitherincrease the number of oxygen holes in the coating layer, which willimprove properties which are dependent upon low emissivity; or it mayserve to reduce the number of oxygen holes in the layer, thus increasingthe emissivity of the coating for certain alternate applications.

The procedure used for heat treating the coated substrate may vary. Inone embodiment the treatment consists of placing the coated substrateinto a heated enclosure under controlled atmospheric conditions for apredetermined period, depending upon the temperature chosen for theenclosure and the nature of the atmosphere utilized. In order to improvethose properties dependent upon low emissivity values, this heattreatment takes place in a reducing atmosphere, which may be identicalwith that of the float bath, i.e. 90% nitrogen and 10% hydrogen or,optionally, a neutral atmosphere.

By heat treating the coated substrate in a reducing or neutralatmosphere, an anionic doping effect is produced which is favorable toincreasing the electrical conduction and infrared reflection of thelayer. Depending upon the time interval and temperature selected, thedensity of the charge carriers can be varied considerably from, forexample, 1×10²⁰ to 15×10²⁰ carriers per cm³. The mobility of the chargecarriers may also be varied, for example, from 10 to 50 cmV⁻¹ s⁻¹.

The heat treatment described above may be performed immediately afterthe formation of the oxide layer, directly on the glass production lineas, for example, in an annealing lehr, to advantageously incorporate theheat of the glass into the process. Alternatively, this step may also beperformed later in a separate installation on the glass production line,such as an attached tunnel lehr or a tempering or bending line.

In performance of this heat treatment, the coated substrate must beheated to a temperature of at least 300° C., keeping in mind that thetemperature chosen must be compatible with the substrate. The durationof this heating step is adjusted depending upon the temperature chosen,as well as the composition of the reducing atmosphere and it may rangefrom a few seconds to several hours. The item is then cooled to atemperature no higher than 300° C. until contact with an oxidizingatmosphere no longer alters the performance of the layer. In cases wherethe treatment is performed simultaneously with the tempering of theglass, the nozzles which supply the tempering gasses may also beconnected to sources supplying the reducing or neutral gas necessary forthe treatment.

The efficiency of the heat treatment increases with:

the reducing nature of the atmosphere in the heating enclosure. Forexample, with the percentage of hydrogen in a mixture of N₂ +x% H₂wherein X is a positive real number or 0, most advantageously when Xranges between 0 and 10 for a treatment improving the low emissivityproperties;

the temperature, advantageously ranging between 300° and 650° C.; and

the time chosen for the treatment, which can range between a few secondsand several hours, depending upon the temperature chosen and thecomposition of the atmosphere used within the enclosure.

Alternatively, the heat treatment in an enclosure may be performed in anoxidizing atmosphere in order to increase the emissivity of the coating.

In another embodiment of this heat treatment process, the oxide mayeither be reduced until a metal by passing the coated substrate througha reducing burning stream or, alternatively, the substoechiometric metaloxide layer may be oxidized by passing the coated substrate through anoxidizing burning stream. Advantageously, the coated substrate issubjected to this intense heating for a period of less than one second.Depending upon whether one chooses a reducing or oxidizing gas mixturefor the burner jet, one may increase, or, on the contrary, reduce thoseproperties of the layer thus treated which depend upon low emissivity.

By utilizing the process described above, the average temperaturereached by the substrate may be as low as 70° C. if the burner isarranged so that the flame impinges upon the substrate only on thecoated side. This assures that a previously tempered glass substrateretains its tempering level and that heat-sensitive substratesmanufactured of a material other than glass or comprising, in additionto the glass, other materials such as polyvinyl butyrals (PVB's) are notadversely affected.

The burner utilized for treating the coating layer, which is describedin detail below, is fed a mixture of comburent gas (e.g. oxygen or amixture of a neutral gas and oxygen) and a combustible gas containinghydrogen and/or carbon (e.g. hydrogen, carbon monoxide or a gaseousalkane, alkene or alkyne). The proportions of the comburent andcombustible gasses are not stoichiometric. On the contrary, the mixturecontains an excess of a reducing gas or an oxidizing gas, depending uponwhether a reducing treatment or an oxidizing treatment is desired. Theburner described below may be, for reasons of safety and ease of use, alinear burner with outside gas mixing.

The burner 10 is of the type shown in the accompanying drawing figure.It is constructed of two chambers 12, 14 for the introduction of thecombustible and comburent gases, which are fed into burner 10 by pipes16 and 18. Each of chambers 12, 14 is provided with access vents 20, 22to the surface of burner 10. Vents 20 which permit the flow of gas fromupper chamber 14 communicate with chamber 2 by means of pipes 24 whichpass through lower chamber 12 in an airtight configuration.

In order to promote an effective mixing of the combustible and comburentgasses, vents 20 and 22 are oriented in a zig-zag configuration on thesurface of burner 10. If burners of a greater length are necessary for aparticular application, a deflector (not illustrated) may be provided orchambers 12 and 14 may be constructed with a beveled shape in order toassure an equality of distribution of the gasses from one end of burner10 to the other. Burners of this type are manufactured by the Frenchcompany AIR LIQUIDE under the trade name "FMT burners".

As noted above, after spraying the indium formate powder on the surfaceof the substrate, alone or in combination with tin compounds such asdibutyltin oxide and dibutyltin fluoride, the resulting coating is alsooxidized to have good low emissivity and low resistivitycharacteristics, and a heat treatment of the coated substrate isnecessary to improve these characteristics. The proportions of oxidizingor reducing gasses chosen for the treatment is a function of theemissivity and resistivity desired, as well as the nature of the gassesand the operating conditions chosen.

One may experimentally determine, for the operating conditions existingat a given installation (e.g. the speed with which the substrate passesthe burners and distance of the substrate from the burners) thenecessary proportions of the gaseous reactants needed to reduce thelayer totally to the metallic state. The attainment of this metallicstate is recognizable due to the fact that once it is reached, the layerchanges in appearance, acquiring a certain mirror-like reflectivity inthe visible spectrum and in some cases, particularly for transformedindium oxide, the coating may begin to lose its adherence to thesubstrate.

This experimental process comprises adjusting the respective proportionsof the oxidizing and reducing gasses so as to provide a mixture thatcontains slightly more reducing gas (i.e. approximately 10%) than theamount necessary for a stoichiometric mixture. Thereafter, variouscoated samples are subjected to the flame treatment while graduallyadjusting the components of the mixture toward stoichiometricproportions, until the coating layer is reduced to the metallic state.The proportions of the gasses necessary to achieve this transition arenoted and one need simply reduce the delivery of the reducing gas fromthis level to attain the desired level of emissivity and reflectivityfor the coating.

EXAMPLES

The following examples are set forth for the purpose of illustrationonly and are not to be construed as limiting the scope of the inventionin any manner.

Examples I-III illustrate the relative proportions of oxygen andhydrogen necessary to effect the heat treatment of a coated substratewhile passing the substrate at various speeds through the heatingchamber.

Example I

A substrate, coated with a powder comprising an indium oxide base, waspassed 1 cm. under the linear burner depicted in the drawing figure at aspeed of 3 cm./second.

In order to obtain optimal emissivity and resistivity properties, thefollowing gas delivery rates were required:

oxygen 1.9 liters/minute/1 cm. of burner length

hydrogen 4.0 liters/minute/1 cm. of burner length

Example II

Under the same conditions described in Example I, an increase in thespeed at which the substrate passes under the burner, to 5 cm./second,requires the following gas delivery rates in order to obtain optimalemissivity and reflectivity:

oxygen 2.3 liters/minute/1 cm. of burner length

hydrogen 4.7 liters/minute/1 cm. of burner length

Example III

When the speed of the substrate is increased further to 20 cm/secondwhile the other parameters described in Examples I and II are unchanged,the following gas delivery rates were required:

oxygen 6.0 liters/minute/1 cm. of burner length

hydrogen 13.0 liters/minute/1 cm. of burner length

Examples IV-IX depict the properties obtained with a composite coatingcomprising a layer of indium formate powder mixed with 4% by weight ofdilutyltin oxide. The heat treatment of the coated substrate in ExamplesIV-VI and IX was carried out using the first method described above,i.e. maintaining the coated substrate in a heated enclosure under acontrolled atmosphere. Examples VII and VIII utilized the second methodof heating to treat the coating described in Examples V and VI, i.e.utilizing a linear burner such as the one depicted in the drawingfigure.

Example IV

A powder comprising an indium formate base was mixed with 4% by weightof dibutyltin oxide and distributed upon a glass ribbon traveling at 18meters/minute, whose surface temperature was maintained at 600° C.

After the resultant pyrolysis of the powder, the coated substrate wassubjected to a heat treatment consisting of an annealing in an enclosureat 600° C. for two minutes under a nonoxidizing nitrogen atmosphere, andthen gradual cooling to 300° C. for two minutes while being maintainedin the nitrogen atmosphere.

The following properties were observed:

    ______________________________________                                                         Before heat                                                                           After heat                                                            treatment                                                                             treatment                                            ______________________________________                                        Thickness (angstroms)                                                                            900       900                                              Aver. Coef. of IR reflection                                                                     0.33      0.70                                             Emissivity         0.67      0.30                                             Transmission energy factor (%)                                                                   74.5      76.0                                             Light transmission factor (%)                                                                    74.3      79.0                                             Square resistance (ohms)                                                                         205       35                                               ______________________________________                                    

Example V

This experiment was performed under the same conditions as Example IV,except that the thickness of the layer deposited upon the substrate wasincreased to 1900 angstroms. The following properties were observed forthis coated substrate:

    ______________________________________                                                         Before heat                                                                           After heat                                                            treatment                                                                             treatment                                            ______________________________________                                        Thickness (angstroms)                                                                            1900      1900                                             Aver. Coef. of IR refiection                                                                     0.53      0.87                                             Emissivity         0.47      0.13                                             Transmission energy factor (%)                                                                   77        72                                               Light transmission factor (%)                                                                    81.3      83.0                                             Square resistance (ohms)                                                                         92        11                                               ______________________________________                                    

Example VI

This experiment was performed under the same conditions as Examples IVand V, except that the thickness of the layer deposited upon thesubstrate was increased to 3000 angstroms. This produced a layer whichwas mauve red in reflection and slightly green in transmission, with thefollowing properties:

    ______________________________________                                                         Before heat                                                                           After heat                                                            treatment                                                                             treatment                                            ______________________________________                                        Thickness (angstroms)                                                                            3000      3000                                             Aver. Coef. of IR reflection                                                                     0.76      0.89                                             Emissivity         0.24      0.11                                             Transmission energy factor (%)                                                                   78.8      66.0                                             Light transmission factor (%)                                                                    85.8      82                                               Square resistance (ohms)                                                                         25        7.5                                              ______________________________________                                    

Example VII

This experiment utilized the same coating described in Example V priorto the heat treatment step. The coated substrate was then subjected tothe flame from a burner of the type described previously. The burner wasfed with a mixture of hydrogen and oxygen as described above.

Upon matching the required gas delivery rate with the speed of thecoated substrate passing beneath the burner flame (see Examples I-III),a coating with the same properties as that in Example V was thereafterobtained.

Example VIII

The coating described in Example VI was deposited upon a glass ribbon,which was then subjected to a heat treatment process as described inExample VII.

A coating with the same properties as described in Example VI wasthereafter obtained.

Example IX

This experiment was performed under the same conditions as Examples IVand V, except that the thickness of the layer deposited upon thesubstrate was increased to 3800 angstroms. The following properties wereobserved for this coated substrate.

    ______________________________________                                                         Before heat                                                                           After heat                                                            treatment                                                                             treatment                                            ______________________________________                                        Thickness (angstroms)                                                                            3800      3800                                             Aver. Coef. of IR reflection                                                                     0.80      0.95                                             Emissivity         0.20      0.05                                             Transmission energy factor (%)                                                                   78.5      65                                               Light transmission factor (%)                                                                    82        78.2                                             Square resistance (ohms)                                                                         20        4.5                                              ______________________________________                                    

These comparative Examples conclusively illustrate that the selection ofeither heat treatment process leads to the formation of a coating uponthe substrate with optimal emissivity and resistivity properties.

Whichever method of heat treatment one selects for the substrate, theheating step may either be performed immediately after the productionand subsequent coating of the glass, for example, on the same floatline, or it may be performed later. This is normally the case when theglass substrate must be tempered or laminated after the coating has beenpyrolytically deposited.

By utilizing either of the two proposed heat treatments with coatingscomprising a mixture of indium formate and either dibutyltin oxide ordibutyltin fluoride, a coating layer may be formed having an electricalresistivity on the order of 2 to 3×10⁻⁴ ohm-cm. By modulating theintensity of the heat treatment, it is also possible to obtain layerperformances intermediate between those of an untreated layer and thosemeasured for a layer which has undergone the most intense heattreatment.

Alternatively, it is also possible to increase the emissivity andresistivity of the layer during the heating process. Thus the resistanceof a coated substrate having a square resistance of 15 ohms may beincreased to 16 ohms, or 2,000 ohms by passing the substrate 1 cm.beneath the burner at 10 cm./second or 6 cm./second respectively. Thegas flow rates utilized to provide these values were 2.4 liters perminute per cm. of burner length for oxygen and 3.0 liters per minute percm. of burner length for hydrogen. The same effect may be obtained byutilizing the first heating procedure described herein in an oxidizing,rather than a reducing atmosphere.

It is also possible with either proposed mode of heat treatment tocreate, on the same coating, zones of different electrical conduction bythe application of different heat treatments. This kind ofdifferentiated heat treatment by zones, on the same coating, isparticularly easy when the second type of heat treatment is used. Forthis purpose, the conditions of exposure of the layer to the heatingmeans are modified locally.

To create this effect, the speed with which the coated substrate to betreated passes the burner is varied as a function of the desired result.With a burner placed crosswise in relation to the direction of travel ofthe substrate, layers with crosswise strips having differentiatedproperties may be obtained by modulating the passing speed of thesubstrate.

It is also possible to obtain lengthwise strips in the direction ofmovement of the substrate with different electrical and opticalcharacteristics by adding additional burners opposite these zones or byperforming the treatment over the entire width of the substrate with aplurality of burners adjusted differently from one another.

These heat treatments, and in particular those performed by the secondmethod utilizing the burners discussed above, are therefore particularlysuited to the production of coatings with layers having zones withdifferentiated electrical, thermal and optical properties. Thus, forexample, heated coatings can be produced with thin layers having varyingresistances, depending upon which zone of the coating one examines.

Alternative methods may be utilized to carry out the heating processdescribed above. For example, a microwave plasma torch fed by reducingor, on the contrary, oxidizing gas, either to reduce the oxide and lowerthe emissivity or resistivity of the layer, or, on the contrary, tooxidize the metal and increase the emissivity or resistivity of thelayer, may also be utilized.

The second method of heat treatment is therefore particularly suited tothe production of thin-layer coatings for motor vehicle glazings with ahigh level of temper or laminated and enclosing a sheet of plastic, suchas a P.V.B. interlayer. Even if coated and treated according to theinvention, the glazings can be sufficiently tempered to meet the UnitedNations Regulation No. 43 for the approval of motor vehicle glazings. Inspite of the tempered treatment the emmissivity and the resistivity ofthese coatings have a good level. The emissivity of the coatings is lessthan 0.15 for a thickness of between 1800-4500 Angstroms and preferablybetween about 1800 to 1900 Angstroms, and the resistivity is less thanor equal to 3×10⁻⁴ ohm/cm.

United Nations Regulations No. 43 contains the requirements for glazingsused in automobiles. Such automobile glazings must be sufficientlytempered, and the required level of tempering is indicated on pages 71and 72 for automobile windshields. Pages 77 and 78 contain therequirements for the other tempered glass panes of an automobile.

The requirements are almost identical for the two types of panes:

(1) when fragmentation tests are performed, the number of fragments inany 5 cm×5 cm square of the tempered pane is not less than 40 nor morethan 350.

(2) however in the case of panes other than windshields and having athickness not more than 3.5 mm the number of fragments can be higher,but must not exceed 400.

This fragmentation shall not be checked in a strip 2 cm wide around theedge of the sample, nor within a radius of 7.5 cm from the point ofimpact. Moreover, fragments of an area exceeding 3 cm² shall not beallowed except in the peripheric zone and around the point of impact asdefined hereabove. A few fragments of elongated shape shall be allowed,provided that they are not more than 7.5 cm long and that their ends arenot knife-edged.

The pyrolytically deposited coatings of the present invention have manyother practical uses, as in, for example, low-emissive glazings, heatedglazings and, in general, glazings making use of the variable opticaland/or electrical properties of the coatings for the building trade;and, as noted earlier, for safety laminates in automotive glass or forauto glass which makes use of the electrical conductivity of the coatingto trigger a burglar alarm when a window is broken, or which constitutesa radio antenna.

The coating of the invention may also be advantageously applied ontovarious substrates, in particular, for insulating glass articles such asbottles, vials, various types of glassware, optical elements, fiberglassand articles comprised of silica, alumina or refractory materials.Standard powder spray guns are used to spray the powder or mixture ofpowders onto the substrates described above, (not the nozzles describedin French patent application nos. 2,542,636 and 2,542,637, discussedearlier).

The indium formate based powders of the invention need not necessarilybe used in solid form. For example, the powder can be solubilized, i.e.in methanol, and the solution may be sprayed directly onto a substratewhereupon it is pyrolyzed and forms a metal oxide layer that can undergoa heat treatment by one of the methods described above in order tomodify the characteristics of the layer.

The heat treatments performed after the deposition of the layer havebeen described as being applied to a layer of indium oxide, whetherdoped or not with tin, and obtained by the pyrolysis of a powder with anindium formate base; but this treatment can also be successfully appliedto any layer with an indium oxide base, whether doped or not with tin orother material, obtained in another way; for example, liquid pyrolysis,CVD (chemical vapor deposition), or a vacuum technique, whether theinitial compound is formate or not.

These heat treatments can even be applied to any other comparatively lowmelting metal layer which, like the layer with an indium oxide base, isnonstoechiometric, thus including, for example, layers with a base ofvanadium, zinc, tin oxide, etc. These heat treatments can even make itpossible to obtain metal layers from metal oxide layers as an endresult. Moreover, the heat treatments may also be used to recrystallizea poorly crystallized or amorphous layer, in order to modify itselectronic properties.

While it is apparent that the invention herein disclosed is wellcalculated to fulfill the objectives above stated, it will beappreciated that numerous modifications and embodiments may be devisedby those skilled in the art, and it is intended that the appended claimscover all such modifications and embodiments as fall within the truespirit and scope of the present invention.

We claim:
 1. A plate of glass coated with a layer consisting essentiallyof indium and tin oxides having zones of a low emissivity andresistivity of less than or equal to 0.15 and 3×10⁻⁴ ohm-cm,respectively for a thickness of between about 1800 and 4500 angstromswith at least one other zone wherein the emissivity and resistivity arehigher than 0.15 and 3×10⁻⁴ ohm-cm, respectively that is producedby:preparing a dry metal composition containing indium formate; mixingat least a powdered or gaseous tin compound or a gaseous organotincompound with the indium formate in proportions ranging from one tothirty weight percent; depositing said composition onto a surface of aheated glass plate so as to pyrolyze the composition; and heating thecoated glass plate to enhance the properties of the layer.
 2. A plate ofglass coated with a pyrolyzed metal oxide layer consisting essentiallyof indium oxide formed by depositing a predetermined amount of a dry,powdered organic indium compound on the heated glass plate, therebypyrolyzing the indium compound; wherein the layer comprises a first zonehaving an emissivity of less than or equal to 0.15 and a resistivity ofless than or equal to 3×10⁻⁴ ohm-cm, and a second zone having aemissivity greater than 0.15 and a resistivity greater than 3×10⁻⁴ohm-cm.
 3. The glass plate of claim 2, wherein the thickness of thelayer is between about 1800 to 4500 Angstroms.
 4. The glass plate ofclaim 2, wherein the metal oxide layer further comprises oxides of anelectrically conductive metal formed by combining at least one compoundof the electrically conductive metal with the organic indium compoundand depositing the combined compounds on the substrate.
 5. The glassplate of claim 4, wherein the at least one electrically conductive metalcompound has a decomposition temperature on the same order as the indiumcompound.
 6. The glass plate of claim 5, wherein the at least oneelectrically conductive metal compound is selected from the groupconsisting of powdered or gaseous tin compounds and gaseous organotincompounds.
 7. The glass plate of claim 6, wherein the indium compound isdry and powdered.
 8. The glass plate of claim 6, wherein the powderedtin compounds are added in proportions ranging from one to thirty weightpercent and are selected from the group consisting of dibutyltin oxideand dibutyltin fluoride.